Panel driving circuit that generates panel test pattern and panel test method thereof

ABSTRACT

A panel driving circuit that produces a panel test pattern and a method of testing a panel are provided. The driving circuit includes a pattern generation unit and a selection unit. The pattern generation unit responds to a system clock and produces pattern test data and pattern test signals. The selection unit responds to a test signal and selects and outputs either (a) the pattern test data and the pattern test signals that are outputted from the pattern generation unit, or (b) the pattern test data and pattern test signals that are directly applied from the outside. The driving circuit and the method of the panel test generates the panel test data, the horizontal synchronizing signal, the vertical synchronizing signal, and the data activating signal within the driving circuit using a system clock so that the testing of the panel can be carried out without using a separate test device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. patent application Ser. No.13/085,800, filed Apr. 13, 2011, now U.S. Pat. No. 8,055,968 which is aContinuation Application of U.S. patent application Ser. No. 12/616,466,filed Nov. 11, 2009, now abandoned which is a Continuation Applicationof U.S. Pat. No. 7,627,799, filed Jan. 28, 2005, which in turn claims topriority of Korean Patent Application No. 2004-5597, filed on Jan. 29,2004, in the Korean Intellectual Property Office, the disclosures ofwhich are incorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates liquid crystal displays, and moreparticularly, to a panel driving circuit that generates pattern testdata and pattern test signals for testing a panel, and a method oftesting the panel using the panel driving circuit.

2. Description of the Related Art

FIG. 1 is a block diagram of a conventional liquid crystal display (LCD)panel driving system. Referring to FIG. 1, the conventional LCD paneldriving system 100 includes a driving circuit 120, a graphic processor130, a memory 140, a Central Processing Unit (CPU) 150, and peripheralcircuits 160 and 170. The CPU 150 applies a control signal S_COM to thegraphic processor 130 to control the panel 110 and the driving circuit120. The memory 140 applies data DATA to the graphic processor 130. Inresponse to the control signal S_COM outputted from the CPU 150 and thedata DATA outputted from the memory 140, the graphic processor 130applies a horizontal synchronizing signal HSYNC, a verticalsynchronizing signal VSYNC, the data DATA, a system clock DCLK, and anyof a variety of other inputs to the driving circuit 120 to drive thepanel 110.

In response to the horizontal synchronizing signal HSYNC, the verticalsynchronizing signal VSYNC, the data DATA, and the system clock DCLKinputted to the driving circuit 120, the driving circuit 120 produces agate line control signal S_GATE and a source line control signalS_SOURCE that control a gate line (not shown) and a source line (notshown) of the panel 110, respectively. When the gate line of the panel110 is turned on by the gate line control signal S_GATE, the data DATAis applied to the panel 110 through the source control signal S_SOURCE.

There are two operation modes of the driving circuit 120. One is a CPUinterface mode in which the driving circuit 120 interfaces directly withthe CPU 150 and receives the control signal S_COM from the CPU 150directly (not shown in FIG. 1). The other, a shown in FIG. 1, is a videointerface mode in which the graphic processor 130 exists between thedriving circuit 120 and the CPU 150 and the driving circuit 120interfaces directly with the graphic processor 130. A driving circuitthat operates in the video interface mode is widely used in displaydevices of mobile communications devices like mobile phones.

An alternate version of the driving circuit 120 has fewer circuits thatthe CPU 150 controls and reduces the burden on the CPU 150. As a result,the alternate version of the driving circuit 120 usually adapts thevideo interface mode that interfaces directly with the graphic processor130 Further, the alternate version of the driving circuit 120 can embodyvarious image functions as well as eliminate problems, such as low imagequality. Low image quality may result from a tearing condition which canoccur in the CPU interface mode while reproducing a moving image. Thedriving circuit 120 of FIG. 1 shows the driving circuit 120 operating inthe video interface mode, in which the driving circuit 120 interfacesdirectly with the graphic processor 130. However, the driving circuit120 of FIG. 1 carries out a test on the panel 110 such as an image test,a reliance test, and the like, by receiving signals needed from aseparate external testing device.

FIG. 2 is a conventional method of testing a panel using the drivingcircuit of FIG. 1. Referring to FIG. 2, a driving circuit 220 receivessignals needed to test a panel 210 from an external testing device 230.

When testing the panel 210, a test pattern S_PATTERN such as gray,cross-talk, and flicker patterns are applied to the panel 210 to checkwhether the panel 210 displays the test pattern S_PATTERN correctly. Thedriving circuit 220 receives a vertical synchronizing signal VSYNC, ahorizontal synchronizing signal HSYNC, a system clock DCLK, a dataactivating signal DE, and data DATA and generates the test patternS_PATTERN and applies the test pattern S_PATTERN to the panel 210.

Thus, the testing of the panel 210 using the conventional drivingcircuit 220 becomes more complex. The conventional driving circuit 220receives signals for generating the test pattern S_PATTERN from theexternal testing device 230. As a result, the conventional drivingcircuit 220 must consider the conditions of the external testing device230 and the interface between the conventional driving circuit 220 andthe external testing device 230.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided adriving circuit that includes a pattern generation unit and a selectionunit. The pattern generation unit produces pattern test data and patterntest signals in response to a system clock. The selection unit choosesand outputs one of the pattern test data and the pattern test signalsthat are outputted from the pattern generation unit, and pattern testdata and pattern test signals that are applied directly from theoutside.

The pattern test data is data used to test an external panel, and thepattern test signals are a horizontal synchronizing signal, a verticalsynchronizing signal, and a data activating signal with which thepattern test data is synchronized.

The pattern generation unit includes a first counter, a horizontalsynchronizing signal generation unit, a data activating signalgeneration unit, a second counter, a vertical synchronizing signal, athird counter, a pattern decision making unit, and a data storage unit.The first counter calculates and outputs the number of cycles of thesystem clock. The horizontal synchronizing signal generation unitreceives the output of the first counter and produces the horizontalsynchronizing signal whenever the output of the first counter reaches apredetermined value. The data activating signal generation unit receivesthe output of the first counter and produces the data activating signalwhenever the output of the first counter reaches a predetermined value.The second counter calculates the number of cycles of the horizontalsynchronizing signals. The vertical synchronizing signal receives theoutput of the second counter and produces the vertical synchronizingsignal whenever the output of the second counter reaches a predeterminedvalue. The third counter calculates the number of cycles of the verticalsynchronizing signals. The pattern decision making unit responds to theoutput of the third counter and produces a pattern signal that decideswhich test pattern will check the panel. The data storage unit respondsto the output of the second counter and the pattern signal and outputsthe pattern test data.

The predetermined value of the horizontal and the vertical synchronizingsignal generation units are decided by the size of the panel. The dataactivating signal is activated during the cycle of the horizontalsynchronizing signal except for a certain amount of time after thehorizontal synchronizing signal is produced and before the next cycle ofthe horizontal synchronizing signal is to be produced.

The pattern decision making unit includes a plurality of the testpatterns that is for examining the panel. The panel driving circuit canfurther include a control unit that receives the pattern test data, thepattern test signals, and the system clock, which are outputted from theselection unit, and applies the pattern test data, the pattern testsignals, and the system clock to the external panel.

According to another aspect of the present invention, there is provideda method of testing a panel, in which the method of testing the panel ofa driving circuit that generates pattern test data and pattern testsignals to check a panel, includes: determining whether a test signal isactivated or not activated; if the test signal is not activated,applying the pattern test data and the pattern test signals that aredirectly applied from the outside to the panel; and if the test signalis activated, in response to a system clock, generating the pattern testdata and the pattern test signals and applying the pattern test data andthe pattern test signals to the panel.

The generating the pattern test data and the pattern test signals,includes: calculating the number of cycles of the system clock;generating the horizontal synchronizing signal whenever the number ofcycles of the system clock that is calculated reaches a predeterminedvalue; generating the data activating signal whenever the number ofcycles of the system clock reaches a predetermined value; calculatingthe number of cycles of the horizontal synchronizing signal; generatinga vertical synchronizing signal whenever the number of cycles of thehorizontal synchronizing signal reaches a predetermined value;calculating the number of cycles of the vertical synchronizing signal;in response to the vertical synchronizing signal, generating a patternsignal that decides which test pattern will check the panel; and inresponse to the number of cycles the horizontal synchronizing signalsand the pattern signal, outputting the pattern test data.

The predetermined value to generate the horizontal synchronizing signaland the vertical synchronizing signal is decided based on the size ofthe panel. The data activating signal is activated during the cycle ofthe horizontal synchronizing signal except for a certain amount of timeafter the horizontal synchronizing signal is produced and before thenext cycle of the horizontal synchronizing signal is to be produced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is a block diagram of a conventional liquid crystal display (LCD)panel driving system;

FIG. 2 is a conventional method of testing a panel using the drivingcircuit of FIG. 1;

FIG. 3 is a block diagram of a driving circuit according to an exemplaryembodiment of the present invention;

FIG. 4 is a block diagram of the pattern generation unit of FIG. 3;

FIG. 5A is a view of a waveform of horizontal and vertical synchronizingsignals, respectively, which are outputted from the pattern generationunit of FIG. 3;

FIG. 5B is a view showing a relationship between a data activatingsignal, a horizontal synchronizing signal, pattern test data and asystem clock, respectively;

FIG. 6 is a flow chart of a method of testing a panel according to anexemplary embodiment of the present invention; and

FIG. 7 is a flow chart explaining the Operation 630 of FIG. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 3 is a block diagram of a driving circuit according to an exemplaryembodiment of the present invention. Referring to FIG. 3, a drivingcircuit 300 according to an exemplary embodiment of the presentinvention includes a pattern generation unit 310 and a selection unit320.

The pattern generation unit 310 responds to a system clock DCLK andgenerates pattern testing data DATA and pattern test signals HSYNC,VSYNC and DE. The selection unit 320 responds to a test signal TESTENand selects and outputs either the pattern test data DATA and thepattern test signals HSYNC, VSYNC, and DE outputted from the patterngeneration unit 310 or pattern test data DATA and pattern test signalsHSYNC, VSYNC, and DE that are directly applied from the outside.

Here, the pattern test data DATA is to test an external panel 340 andthe pattern test signals HSYNC, VSYNC, and DE are a horizontalsynchronizing signal HSYNC, a vertical synchronizing signal VSYNC, and adata activating signal DE, with which the pattern test data DATA issynchronized.

FIG. 6 is a flow chart of a method of testing a panel according to anexemplary embodiment of the present invention. FIG. 7 is a flow chartexplaining the Operation 630 of FIG. 6.

Referring to FIG. 6, a method 600 of testing a panel according to anexemplary embodiment of the present invention determines whether a testsignal is activated or not activated (Operation 610). If the test signalis not activated, test data and pattern test signals that are directlyapplied from the outside are applied to a panel (Operation 620). If thetest signal is activated, pattern test data and pattern test signals aregenerated and applied to the panel (Operation 630) in response to asystem clock.

An operation of a driving circuit and a method of testing a panelaccording to an exemplary embodiment of the present invention will bedescribed below with reference to FIGS. 3 through 7.

First, it is determined whether the test signal TESTEN is activated ornot (Operation 610). If the test signal TESTEN is not activated, thetest data DATA and the pattern test signals HSYNC, VSYNC, and DE thatare directly applied from the outside are applied to the panel 340(Operation 620).

Operations 610 and 620 are carried out in the selection unit 320 of FIG.3. The selection unit 320 responds to the test signal TESTEN, and if thetest signal TESTEN is not activated, the selection unit 320 selects andoutputs the pattern test data DATA, the horizontal synchronizing signalHSYNC, the vertical synchronizing signal VSYNC, and the data activatingsignal DE that are applied from the outside.

The pattern test data DATA, the horizontal synchronizing signal HSYNC,the vertical synchronizing signal VSYNC, and the data activating signalDE that are outputted from the selection unit 320 are received by acontrol unit 330 in response to the system clock DCLK. The control unit330 receives the pattern test data DATA, the horizontal synchronizingsignal HSYNC, the vertical synchronizing signal VSYNC, and the dataactivating signal DE and applies them to the external panel 340 as atest pattern S_PATTERN.

In response to the test pattern S_PATTERN, the panel 340 displays animage that corresponds to the test pattern S_PATTERN. There are manytypes of the test pattern S_PATTERN. For example, there is a graypattern in which the entire panel 340 looks gray, a cross-talk patternwhich makes the panel 340 look as if there is a black quadrangle insidea gray background, and the like.

If the test signal TESTEN is activated, the pattern test data DATA andthe pattern test signals HSYNC, VSYNC, and DE are generated and appliedto the panel 340 (Operation 630) in response to the system clock DCLK.

Operation 630 is carried out in the pattern generation unit 310 of FIG.3. That is, if the test signal TESTEN is activated, the selection unit320 receives the pattern test data DATA, the horizontal synchronizingsignal HSYNC, the vertical synchronizing signal VSYNC, and the dataactivating signal DE that are outputted from the pattern generation unit310, and the selection unit 320 outputs the pattern test data DATA, thehorizontal synchronizing signal HSYNC, the vertical synchronizing signalVSYNC, and the data activating signal DE to the control unit 330. Thepattern generation unit 310 receives the system clock DCLK and outputsthe pattern test data DATA, the horizontal synchronizing signal HSYNC,the vertical synchronizing signal VSYNC, and the data activating signalDE.

FIG. 4 is a block diagram of the pattern generation unit 310 of FIG. 3.FIG. 5A is a view of the waveforms of the horizontal and verticalsynchronizing signals HSYNC and VSYNC, respectively, that are outputtedfrom the pattern generation unit 310 of FIG. 3 and FIG. 5B is a viewshowing a relationship between the data activating signal DE, thehorizontal synchronizing signal HSYNC, and the pattern test data DATAand the system clock DCLK, respectively.

Referring to FIG. 4, the pattern generation unit 310 includes a firstcounter 410, a horizontal synchronizing signal generation unit 420, adata activating signal generation unit 430, a second counter 440, avertical synchronizing signal generation unit 450, a third counter 460,a pattern decision making unit 470, and a data storage unit 480.

The horizontal synchronizing signal HSYNC, the vertical synchronizingsignal VSYNC, and the data activating signal DE all have a predeterminedrelationship with the system clock DCLK. In other words, when the numberof clock cycles of the system clock DCLK reaches a predetermined number,the horizontal synchronizing signal HSYNC is activated. Also, wheneverthe horizontal synchronizing signal HSYNC is produced for a certaintime, the vertical synchronizing signal VSYNC is generated. The dataactivating signal DE also has a predetermined relationship with thehorizontal synchronizing signal HSYNC. Therefore, the horizontalsynchronizing signal HSYNC, the vertical synchronizing signal VSYNC, andthe data activating signal DE can be generated from the system clockDCLK.

The driving circuit 300 of FIG. 3 includes the pattern generation unit310 that generates signals such as the horizontal synchronizing signalHSYNC, the vertical synchronizing signal VSYNC, and the data activatingsignal DE using the system clock DCLK. This is unlike the conventionaldriving circuit, as described in greater detail above in FIG. 2, inwhich signals such as the horizontal synchronizing signal HSYNC, thevertical synchronizing signal VSYNC, and the data activating signal DEare received through an external testing device 230. Consequently, thedriving circuit 300 of FIG. 3, without the need for any separate,external testing device, can test the panel 340 by outputting the testpattern S_PATTERN needed for testing the panel 340.

Operation 630 includes Operation 710 which calculates the number ofclock cycles of the system clock DCLK. Operation 710 is carried out bythe first counter 410 of FIG. 4. In other words, the first counter 410of the pattern generation unit 310 calculates and outputs the number ofclock cycles of the system clock DCLK.

Then, whenever the calculated number of clock cycles of the system clockDCLK reaches a predetermined value, the horizontal synchronizing signalHSYNC is generated (Operation 720). Operation 720 is carried out by thehorizontal synchronizing signal generation unit 420. The horizontalsynchronizing signal generation unit 420 receives the output of thefirst counter 410, and whenever the output of the first counter 410reaches a predetermined value, the horizontal synchronizing signal HSYNCis produced.

The predetermined value of the first counter 410 to generate thehorizontal synchronizing signal HSYNC is determined by the size of thepanel 340. For example, it is presumed that a single horizontal line ofthe panel 340 has 192 system clock cycles. The horizontal synchronizingsignal HSYNC is activated at each horizontal line of the panel 340.Therefore, the horizontal synchronizing signal generation unit 420receives the output from the first counter 410, and when the output ofthe first counter 410 reaches 192, the horizontal synchronizing signalgeneration unit 420 generates the horizontal synchronizing signal HSYNC.

Whenever the number of clock cycles of the system clock DCLK reaches apredetermined value, the data activating signal DE is produced(Operation 730). Operation 730 is carried out by the data activatingsignal generation unit 430 of FIG. 4.

The data activating signal generation unit 430 receives the output ofthe first counter 410 and whenever the output of the first counter 410reaches a predetermined value, the data activating signal DE isproduced. The data activating signal DE is activated during the cycle ofthe horizontal synchronizing signal HSYNC except for a certain amount oftime after the horizontal synchronizing signal HSYNC is produced andbefore the next cycle of the horizontal synchronizing signal HSYNC is tobe produced.

If it is assumed that the certain amount of time before and after thehorizontal synchronizing signal HSYNC during which the data activatingsignal DE is not activated is 8 system clock DCLK cycles each, the dataactivating signal DE is activated for 176 system clock DCLK cycles andnot activated for the rest of the clock cycles, i.e., for 16 systemclock DCLK cycles. A waveform of the data activating signal DE isillustrated in FIG. 5B.

Next the number of clock cycles of the horizontal synchronizing signalsHSYNC is counted (Operation 740). Operation 740 is carried out by thesecond counter 440 of FIG. 4. That is, the second counter 440 calculatesthe number of cycles of the horizontal synchronizing signals HSYNC.

Whenever the number of cycles of the horizontal synchronizing signalHSYNC reaches a predetermined value, the vertical synchronizing signalVSYNC is produced (Operation 750). Operation 750 is carried out by thevertical synchronizing signal generation unit 450 of FIG. 4. Thevertical synchronizing signal generation unit 450 receives the output ofthe second counter 440 and whenever the output of the second counter 440reaches a predetermined value, the vertical synchronizing signalgeneration unit 450 produces the vertical synchronizing signal VSYNC.

The predetermined value of the second counter 440 to produce thevertical synchronizing signal VSYNC is determined by the size of thepanel 340. For example, it is assumed that a single field of the panel340 has 256 horizontal lines. A single vertical synchronizing signalVSYNC is produced for each field of the panel 340. Therefore, thevertical synchronizing signal generation unit 450 receives the output ofthe second counter 440 and when the output of the second counter 440reaches 256, the vertical synchronizing signal VSYNC is produced. Arelationship between the horizontal and vertical synchronizing signalsHSYNC and VSYNC is illustrated in FIG. 5A.

Next the number of the vertical synchronizing signals VSYNC iscalculated (Operation 760). Operation 760 is carried out by the thirdcounter 460 of FIG. 4.

In response to the number of the vertical synchronizing signal VSYNC, apattern signal S_PAT, which determines the test pattern that is to checkthe panel 340, is generated (Operation 770). Operation 770 is carriedout by the pattern decision making unit 470 of FIG. 4.

In response to the output of the third counter 460, the pattern decisionmaking unit 470 determines a test pattern to check the panel 340. Thepattern decision making unit 470 has a number of test patterns to checkthe panel 340.

The output of the third counter 460 shows the number of cycles of thevertical synchronizing signal VSYNC. Whenever the output of the thirdcounter 460 increases incrementally by one, a single field (not shown)of the panel 340 changes. The single field of the panel 340 refers to asingle screen that is displayed on the panel 340.

The pattern decision making unit 470 has a number of test patterns suchas a cross-talk pattern and a gray pattern. Also, in response to theoutput of the third counter 460, the pattern decision making unit 470decides which test pattern, i.e., which image, is to be shown on thepanel 340.

Whenever the output of the third counter 460 increases incrementally byone, the test pattern may change. Also, whenever the output of the thirdcounter 460 increases incrementally two, the test pattern may change.

If the test pattern is changed whenever the output of the third counter460 increases incrementally by one, the test pattern, i.e., the image,that is displayed on the screen will change whenever the screen of thepanel 340 changes once. If the test pattern is changed whenever theoutput of the third counter 460 increases incrementally by two, the testpattern, i.e., the image, will change whenever the screen of the panel340 changes twice. The designer of the driving circuit 300 decides thenumber of screen changes of the panel 340 corresponding to the changesof the test pattern.

In response to the predetermined number of cycles of the horizontalsynchronizing signal HSYNC and the pattern signal S_PAT, the patterntest data DATA is output (Operation 780). Operation 780 is carried outby the data storage unit 480. The data storage unit 480 responds to theoutput of the second counter 440 and the pattern signal S_PAT andoutputs the pattern test data DATA.

The pattern signal S_PAT has information on the test pattern, i.e., theimage, that is to be displayed on the screen of the panel 340. Inaddition, the second counter 440 calculates the number of cycles of thehorizontal synchronizing signal HSYNC.

The data storage unit 480 saves data and outputs the data needed foreach of the horizontal lines as the pattern test data DATA so that theimage corresponding to the pattern signal S_PAT can be shown on thepanel 340.

It is supposed that the test data pattern that corresponds to thepattern signal S_PAT makes the entire panel 340 look gray with a blackquadrangle in the middle. In response to the output of the secondcounter 440, the data storage unit 480 outputs pattern test data DATA tomake from the 1^(st) through 85^(th) horizontal line and from the170^(th) through 256^(th) horizontal line among 256 horizontal lines ofthe panel 340 to be displayed as gray. Additionally, the data storageunit 480 outputs pattern test data DATA to be displayed as gray, black,and gray sequentially for each horizontal line from the 86^(th) through169^(th) horizontal lines. As such, the data storage unit 480 has thepattern signal S_PAT that has information on the image to be shown onthe panel 340. Further, the data storage unit 480 responds to the numberof cycles of the horizontal synchronizing signal HSYNC and outputs thepattern test data DATA.

As previously described in FIG. 3, according to the driving circuit 300of the exemplary embodiment of the present invention, when the testsignal TESTEN is not activated, the pattern test data DATA and thepattern test signals HSYNC, VSYNC, and DE that are transmitted from theoutside are applied to the panel 340. When the test signal TESTEN isactivated, the pattern test data DATA and the pattern test signalsHSYNC, VSYNC, and DE that are outputted from the pattern generation unit310 within the driving circuit 300 are applied to the panel 340. Thatis, as the driving circuit 300 controls the test signal TESTEN, thedriving circuit 300 can either use the conventional method for the paneltest or a method of testing the panel 340 in which the driving circuit300 itself generates the pattern test data DATA and the pattern testsignals HSYNC, VSYNC, and DE.

A driving circuit and a method of testing a panel according to thepresent invention is provided as described above. Panel test data, ahorizontal synchronizing signal, a vertical synchronizing signal, and adata activating signal that are needed for examining the quality of apanel are generated within the driving circuit using a system clock sothat the testing of the panel can be carried out without having to use aseparate test device.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A panel driving circuit that produces a paneltest pattern for testing a panel, the panel driving circuit comprising:a pattern generation unit that produces pattern test data and patterntest signals in response to a system clock; and a selection unit thatchooses and outputs the pattern test data and the pattern test signalsthat are outputted from the pattern generation unit, wherein the patterngeneration unit produces the pattern test signals to display the paneltest pattern generated internally, wherein the pattern test signalscomprise both a vertical synchronizing signal and a horizontalsynchronizing signal, wherein the pattern test data and the pattern testsignals outputted by the selection unit form the panel test pattern inthe panel, the panel test pattern including a gray pattern, a cross-talkpattern, and a flicker pattern, are applied to the panel; and whereinthe vertical synchronizing signal is produced based on a predeterminednumber of the horizontal synchronizing signal.
 2. The panel drivingcircuit of claim 1, wherein the pattern test signals produced by thepattern generation unit further comprise a data activating signal,wherein the pattern test data is synchronized with the data activatingsignal.
 3. The panel driving circuit of claim 2, wherein the dataactivating signal is activated during a cycle of the horizontalsynchronizing signal.
 4. The panel driving circuit of claim 2, whereinthe data activating signal is activated a certain time after thehorizontal synchronizing signal is produced and is deactivated before anext cycle of the horizontal synchronizing signal is produced.
 5. Thepanel driving circuit of claim 1, wherein the selection unit chooses andoutputs the pattern test data and the pattern test signals correspondingto the panel test pattern including the gray pattern, the cross-talkpattern, and the flicker pattern according to a number cycles of thevertical synchronizing signal.
 6. The panel driving circuit of claim 1,further comprising a control unit receiving the pattern test data andthe pattern test signals outputted by the selection unit and outputtingthe pattern test data and the pattern test signals as the panel testpattern in response to the system clock.
 7. A pattern generation unit ofa panel driving circuit, the pattern generation unit comprising: ahorizontal synchronizing signal generation unit producing a cycle of thehorizontal synchronizing signal whenever a number of cycles of a systemclock reaches a predetermined value; a data activating signal generationunit producing a data activating signal whenever the number of cycles ofa system clock reaches a first predetermined value; a verticalsynchronizing signal generation unit producing a cycle of the verticalsynchronizing signal whenever a number of cycles of the horizontalsynchronizing signal reaches a second predetermined value; and a patterndecision making unit producing a pattern signal selecting a test patternwhenever a number of cycles of the vertical synchronizing signal reachesa third predetermined value.
 8. The pattern generation unit of claim 7,wherein the pattern test signals comprise the horizontal synchronizingsignal, the vertical synchronizing signal, and the data activatingsignal with which the pattern test data is synchronized.
 9. The patterngeneration unit of claim 7, wherein the test pattern includes one of agray pattern, a cross-talk pattern, and a flicker pattern, are appliedto a panel.
 10. A panel driving circuit comprising: a pattern generationunit that produces a-pattern test data and a-pattern test signals inresponse to a system clock; and a selection unit that chooses andoutputs the pattern test data and the pattern test signals that areoutputted from the pattern generation unit, wherein the patterngeneration unit calculates the number of cycles of the system clock andproduces the pattern test data and the pattern test signals in responseto the number of cycles of the system clock, wherein the pattern testdata comprises data for testing an external panel, wherein the patterngeneration unit outputs the pattern test data in response to a verticalsynchronizing signal and a horizontal synchronizing signal generated bythe pattern generation unit, wherein the vertical synchronizing signalis produced based on a predetermined number of the horizontalsynchronizing signal.